Parts made of aluminum and magnesium alloys in vehicle body architecture, especially in the passenger compartment safety cage, or greenhouse are used to reduce vehicle weight by including more lightweight alloys that may provide higher strength and increased stiffness. In some applications, lightweight alloy parts must be joined to high strength ferrous material parts to meet design and regulatory requirements. Dissimilar metal joints (such as boron steel to 6xxx series aluminum) are may be specified in structures that are subject to stringent safety standards.
Mechanical joints, such as rivets or clinch joints, may be used to join dissimilar materials but the strength, durability, and corrosion resistance of such joints does not equal the properties of welds between mild steel parts.
Extrusions and hydro-formed parts are advantageously used for the safety cage and specifically the roof rail Body-In-White (BIW) construction because they can offer very high stiffness and improve material utilization compared to assemblies of sheet metal parts with welded flanges. A major roadblock to broad implementation of extrusions and hydro-formed parts is the lack of affordable mass production joining methods to assemble these parts into BIW structures. Joining methods such a resistance welding, MIG welding, TIG welding, friction welding, and spin stir welding generate heat that may introduce dimensional distortion and may detrimentally impact the microstructure or material properties of the parts made of special heat treatable alloys.
Several different types of joining methods are currently available and may be categorized as one-sided or two-sided methods. One-sided joining methods are critical to the implementation of extrusion to extrusion joining because of access problems relating to the closed internal voids in some extrusions. One-sided joining methods such as flow drill screws add cost to the assemblies and are not well suited to high strength steel parts. Two-sided joining methods such as self-piercing rivets and clinch joints require access to the back side of a joint and are difficult to use in some applications where extrusions or tubular parts are joined.
The above problems and other problems are addressed by this disclosure as summarized below.